Human temperature regulation under heat stress in health, disease, and injury

Physiological Reviews, Год журнала: 2022, Номер 102(4), С. 1907 - 1989

Опубликована: Июнь 9, 2022

The human body constantly exchanges heat with the environment. Temperature regulation is a homeostatic feedback control system that ensures deep temperature maintained within narrow limits despite wide variations in environmental conditions and activity-related elevations metabolic production. Extensive research has been performed to study physiological of temperature. This review focuses on healthy disordered during stress. Central this discussion notion various morphological features, intrinsic factors, diseases, injuries independently interactively influence exercise and/or exposure hot ambient temperatures. first sections fundamental aspects stress response, including biophysical principles governing balance autonomic loss thermoeffectors. Next, we discuss effects different factors (morphology, adaptation, biological sex, age), diseases (neurological, cardiovascular, metabolic, genetic), (spinal cord injury, burns, stroke), emphasis mechanisms by which these enhance or disturb We conclude key unanswered questions field research.

Язык: Английский

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Humidity’s Role in Heat-Related Health Outcomes: A Heated Debate

Environmental Health Perspectives, Год журнала: 2023, Номер 131(5)

Опубликована: Май 1, 2023

As atmospheric greenhouse gas concentrations continue to rise, temperature and humidity will increase further, causing potentially dire increases in human heat stress. On physiological biophysical grounds, exposure higher levels of should worsen stress by decreasing sweat evaporation. However, population-scale epidemiological studies response often do not detect associations between high heat-related mortality or morbidity. These divergent, disciplinary views regarding the role health risks limit confidence selecting which interventions are effective reducing impacts projecting future risks.

Язык: Английский

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A physiological approach for assessing human survivability and liveability to heat in a changing climate

Nature Communications, Год журнала: 2023, Номер 14(1)

Опубликована: Ноя. 29, 2023

Most studies projecting human survivability limits to extreme heat with climate change use a 35 °C wet-bulb temperature (Tw) threshold without integrating variations in physiology. This study applies physiological and biophysical principles for young older adults, sun or shade, improve current estimates of introduce liveability (maximum safe, sustained activity) under future climates. Our physiology-based survival show vast underestimation risks by the Tw model hot-dry conditions. Updated correspond Tw~25.8-34.1 (young) ~21.9-33.7 (old)-0.9-13.1 lower than = °C. For female are ~7.2-13.1 dry Liveability declines exposure humidity, yet most dramatically age (2.5-3.0 METs adults). Reductions safe activity younger adults between present indicate stronger impact from aging warming.

Язык: Английский

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Greatly enhanced risk to humans as a consequence of empirically determined lower moist heat stress tolerance

Proceedings of the National Academy of Sciences, Год журнала: 2023, Номер 120(42)

Опубликована: Окт. 9, 2023

As heatwaves become more frequent, intense, and longer-lasting due to climate change, the question of breaching thermal limits becomes pressing. A wet-bulb temperature (T w ) 35 °C has been proposed as a theoretical upper limit on human abilities biologically thermoregulate. But, recent—empirical—research using subjects found significantly lower maximum T at which thermoregulation is possible even with minimal metabolic activity. Projecting future exposure this empirical critical environmental not done. Here, accurate threshold latest coupled model results, we quantify dangerous, potentially lethal heat for climates various global warming levels. We find that humanity vulnerable moist stress than previously because these limits. Still, limiting under 2 nearly eliminates risk widespread uncompensable sharp rise in occurs 3 warming. Parts Middle East Indus River Valley experience brief exceedances only 1.5 More widespread, but brief, dangerous +2 climate, including eastern China sub-Saharan Africa, while US Midwest emerges hotspot +3 climate. In future, extremes will lie outside bounds past beyond current mitigation strategies billions people. While some physiological adaptation from thresholds described here possible, additional behavioral, cultural, technical be required maintain healthy lifestyles.

Язык: Английский

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Exertional heat stroke: pathophysiology and risk factors

BMJ Medicine, Год журнала: 2022, Номер 1(1), С. e000239 - e000239

Опубликована: Окт. 1, 2022

Exertional heat stroke, the third leading cause of mortality in athletes during physical activity, is most severe manifestation exertional illnesses. stroke characterised by central nervous system dysfunction people with hyperthermia activity and can be influenced environmental factors such as heatwaves, which extend incidence beyond athletics only. Epidemiological data indicate rates about 27%, survivors display long term negative health consequences ranging from neurological to cardiovascular dysfunction. The pathophysiology involves thermoregulatory overload, resulting subsequent multiorgan injury due a systemic inflammatory response syndrome coagulopathy. Research risk for remains limited, but dehydration, sex differences, ageing, body composition, previous illness are thought increase risk. Immediate cooling effective treatment strategy. In this review, we provide an overview current literature emphasising highlighting gaps knowledge objective stimulate future research.

Язык: Английский

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Exertional heat stroke in sport and the military: epidemiology and mitigation

Experimental Physiology, Год журнала: 2022, Номер 107(10), С. 1111 - 1121

Опубликована: Авг. 30, 2022

What is the topic of this review? Exertional heat stroke epidemiology in sport and military settings, along with common risk factors strategies policies designed to mitigate its occurrence. advances does it highlight? Individual susceptibility exertional dependent on interaction intrinsic extrinsic factors. Heat should assess environmental conditions, as well characteristics athlete, clothing/equipment worn activity level sport. reduction account for specific training personnel.Exertional illness occurs a continuum, developing from relatively mild condition muscle cramps, exhaustion, some cases life-threatening stroke. The development (EHS) associated an increase core temperature stemming inadequate dissipation offset rate metabolically generated heat. Susceptibility EHS linked several including individual characteristics, health medication drug use, behavioural responses, sport/organisational requirements. Two settings which commonly observed are competitive military. In sport, exact prevalence unclear due inconsistent terminology, diagnostic criteria data reporting. contrast, surveillance facilitated by standardised case definitions, requirement report all centralised medical record repository. To risk, can be implemented athletes personnel, acclimation, ensuring adequate hydration, cold-water immersion mandated work-to-rest ratios. Organisations may also consider or task-specific stress that evaporative loss participants, relative capacity environment. This review examines reduce occurrence settings. We highlight nuances identifying individuals at summarise benefits shortcomings various mitigation strategies.

Язык: Английский

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Epigenetic responses to heat: From adaptation to maladaptation

Experimental Physiology, Год журнала: 2022, Номер 107(10), С. 1144 - 1158

Опубликована: Апрель 12, 2022

New Findings What is the topic of this review? This review outlines history research on epigenetic adaptations to heat exposure. The perspective taken that reflect properties hormesis, whereby low, repeated doses induce adaptation (acclimation/acclimatization); whereas brief, life‐threatening exposures can maladaptive responses. advances does it highlight? mechanisms underlying acclimation/acclimatization comprise specific molecular programmes histones regulate shock proteins transcriptionally and protect organism from subsequent exposures, even after long delays. signalling responses might rely, in part, extensive changes DNA methylation are sustained over time contribute later health challenges. Abstract Epigenetics plays a strong role by producing memory past environmental exposures. Moderate heat, periods time, induces an ‘adaptive’ memory, resulting condition ‘resilience’ future or cross‐tolerance other forms toxic stress. In contrast, intense, such as severe stroke, result ‘maladaptive’ place at risk complications. These cellular memories coded post‐translational modifications nucleosomes and/or methylation. They operate inducing level gene transcription therefore phenotype. adaptive response acclimation functions, facilitating essential exhibits biphasic short programme (maintaining integrity, followed long‐term consolidation). latter accelerates de‐acclimation. Although less studied, stroke appear be long‐lasting near promoter region genes involved with basic cell function. Whether these also encoded histone not yet known. There considerable evidence both inherited, although most comes lower organisms. Future challenges include understanding responsible discovering new ways promote while suppressing all life adapt warming planet.

Язык: Английский

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Age alters the thermoregulatory responses to extreme heat exposure with accompanying activities of daily living

Journal of Applied Physiology, Год журнала: 2023, Номер 135(2), С. 445 - 455

Опубликована: Июль 6, 2023

Using an experimental model of extreme heat exposure that incorporates brief periods light physical activity to simulate activities daily living, the extent thermal strain reported herein more accurately represents what would occur during actual heatwave conditions. Despite matching metabolic generation and environmental conditions, we show older adults have augmented core temperature responses, likely due age-related reductions in dissipating mechanisms.

Язык: Английский

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Classic heat stroke in a desert climate: A systematic review of 2632 cases

Journal of Internal Medicine, Год журнала: 2023, Номер 294(1), С. 7 - 20

Опубликована: Март 23, 2023

Abstract Background Although classic heat stroke (HS) is one of the most ancient conditions known to humans, description its early clinical manifestations, natural course, and complications remains uncertain. Objectives A systematic review demographics, characteristics, biomarkers, therapy, outcomes HS during Muslim (Hajj) pilgrimage in desert climate Mecca, Saudi Arabia. Methods We searched MEDLINE, Embase, Web Science Core Collection, SCOPUS, CINAHL databases from inception April 2022. summarized data eligible studies synthesized them narrative form using pooled descriptive statistics. Results Forty‐four studies, including 2632 patients with HS, met inclusion criteria. Overweight or obesity, diabetes, cardiovascular disease were prevalent among cases HS. Evidence suggests that extreme hyperthermia (pooled mean = 42.0°C [95% confidence interval (CI): 41.9, 42.1], range 40–44.8°C) hot dry skin (>99% cases) severe loss consciousness (mean Glasgow Coma Scale <8 53.8% dominant characteristics Hypotension, tachypnea, vomiting, diarrhea, biochemical biomarkers indicating mild‐to‐moderate rhabdomyolysis, acute kidney, liver, heart injury, coagulopathy frequent at onset. Concomitantly, stress hormones (cortisol catecholamines) systemic inflammation coagulation activation increased. was fatal 1 18 case fatality rate 5.6% [95%CI: 4.6, 6.5]). Conclusions The findings this suggest induces an multiorgan injury can progress rapidly organ failure, culminating death, if it not recognized treated promptly.

Язык: Английский

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Optimal heat stress metric for modelling heat‐related mortality varies from country to country

International Journal of Climatology, Год журнала: 2023, Номер 43(12), С. 5553 - 5568

Опубликована: Июль 12, 2023

Abstract Combined heat and humidity is frequently described as the main driver of human heat‐related mortality, more so than dry‐bulb temperature alone. While based on physiological thinking, this assumption has not been robustly supported by epidemiological evidence. By performing first systematic comparison eight stress metrics (i.e., combined with other climate variables) warm‐season in 604 locations over 39 countries, we find that optimal metric for modelling mortality varies from country to country. Temperature no or little modification associates best ~40% studied countries. Apparent (combined temperature, wind speed) dominates another 40% There obvious grouping these results. We recommend, where possible, researchers use each However, performs similarly humidity‐based estimating present‐day climate.

Язык: Английский

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